In this study, we investigated the influence of Na content on secondary phases and current pathway in Cu-2(Zn,Sn)Se-4 (CZTSe) thin film solar cells with the following structure: Ti/Mo:Na/Mo/CZTSe/CdS/i-ZnO/ ZnO:Al/Al. The application of Na-doped Mo target as a source of sodium. Experimental results demonstrate that increasing the Na content leads to an increase in the quantity of secondary phase SnSe2 on the surface of the absorber layer; however, it did not appear to affect the secondary phases of Cu2SnSe3 (CTSe) or ZnSe. Excessive quantities of Na were shown to have an adverse effect on device efficiency. Our results using conductive atomic force microscopy (C-AFM) revealed that an increase in the quantity of secondary phase SnSe2 can shift the current pathway on the surface of CZTSe from CZTSe grain boundaries (GBs) to the SnSe2 grains. The role of secondary phase SnSe2 of the CZTSe acted as a channel for the current flow, which results in high leakage current and low device efficiency. (C) 2017 Elsevier B.V. All rights reserved.